The present invention pertains to the field of display devices. More specifically, the present invention is related to the field of gamma correction and white-balance adjustment in flat panel displays.
Flat panel liquid crystal displays (LCDs) are popular display devices for conveying information generated by a computer system. The decreased weight and size of a flat panel display greatly increases its versatility over a cathode ray tube (CRT) display. Fiat panel LCD monitors are used today in many applications including the computer component and computer periphery industries where flat panel LCD monitors are an excellent display choice for lap-top computers and other portable electronic devices. Because flat panel LCD technology is improving, more and more flat panel LCD monitors are rapidly replacing CRT displays in other mainstream applications, such as desktop computers, high-end graphics computers, and as televisions and other multi-media monitors.
In flat panel LCD monitors, much like conventional CRT displays, a white pixel is composed of a red, a green and a blue color point or xe2x80x9cspot.xe2x80x9d When each color point of the pixel is excited simultaneously and with the appropriate energy, white can be perceived by the viewer at the pixel screen position. To produce different colors at the pixel, the intensity to which the red, green and blue points are driven is altered in well known fashions. The separate red, green and blue data that corresponds to the color intensities of a particular pixel is called the pixel""s color data. Color data is often called gray scale data. The degree to which different colors can be achieved within a pixel is referred to as gray scale resolution. Gray scale resolution is directly related to the amount of different intensities, or shades, to which each red, green and blue point can be driven.
The method of altering the relative color intensities of the color points across a display screen is called white balance adjustment (also referred to as color balance adjustment, color temperature adjustment, white adjustment, or color balancing). In a display, the xe2x80x9ccolor temperaturexe2x80x9d of white correlates to the relative percentage contributions of its red, green and blue intensity components. In addition, the xe2x80x9ccolor temperaturexe2x80x9d of white correlates to the luminous energy given off by an ideal black body radiating sphere at a particular temperature expressed in degree Kelvin (K). Relatively high degree K color temperatures represent xe2x80x9cwhitexe2x80x9d having a larger blue contribution (e.g., a xe2x80x9ccoolerxe2x80x9d look). Relatively small degrees K color temperatures represent xe2x80x9cwhitexe2x80x9d having a larger red contribution (e.g., a xe2x80x9cwarmerxe2x80x9d look). Generally, the color temperature of a display screen is adjusted from blue to red while avoiding any yellowish or green-ish variations within the CIE chromaticity diagram.
In conventional CRT devices, white balance is adjusted by independently altering the voltage gains of the primary electron guns (e.g., red, green and blue guns) depending on the desired color temperature. However, this prior art color balancing technique reduces the dynamic gray scale range of some or all of the RGB colors, as well as the overall color gamut of the display. In some conventional flat panel LCDs, a shift in color temperature may be achieved by adjusting the relative intensities of the RGB gray levels in a manner analogous to the adjusting of the gain of the electron guns of the CRT devices. However, this prior art method also causes the LCDs to lose dynamic gray scale range and color gamut.
Another prior art method of adjusting the white balance within a flat panel LCD screen pertains to altering the physical color filters used to generate the red, green and blue color points. By altering the color of the filters, the color temperature of the LCD screen can be adjusted. However, this adjustment is not dynamic because the color filters need to be physically (e.g., manually) replaced each time adjustment is required. It would be advantageous to provide a color balancing mechanism for a flat panel LCD screen that can respond, dynamically, to required changes in the color temperature of the display.
The white balance adjustment for a display is important because many users want the ability to alter the display""s color temperature for a variety of different reasons. For instance, the color temperature might be varied based on a viewer""s personal taste. In other situations, color temperature adjustment may be needed to compensate for manufacturing variations in the display. In some situations, color temperature adjustment can correct for the effects of aging in some displays. Particularly, color critical applications such as pre-press soft proofing, desktop publishing, graphics design, medical imaging, and, digital photography and video editing, etc., require white balance values and gamma values of different displays to be precisely matched in order to accurately view and exchange images with confidence. Thus, without an efficient and effective method of providing dynamic white balance adjustment capabilities, flat panel LCDs have heretofore been unused in color critical applications which require precise color calibration and matching. Therefore, what is, needed is an efficient and effective method of providing dynamic white balance adjustment capabilities in flat panel LCDs.
Accordingly, the present invention provides a display for mechanism and method for dynamically adjusting the color balance of a flat panel liquid crystal display without compromising the gray-scale resolution of the pixels. Further, the present invention provides a mechanism and method for adjusting the color balance of a flat panel display screen without complicated circuitry. Embodiments of the present solution also performs gamma correction and frame rate time domain modulation to reduce scalloping and visual artifacts. These and other advantages of the present invention not specifically mentioned above will become clear within discussions of the present invention presented herein.
A system and method are described herein for controlling the white balance and providing gamma correction without compromising gray-scale resolution in a flat panel liquid crystal display (LCD). According to one embodiment of the present invention, the flat panel LCD includes electronic circuitry for coupling to a host computer to receive a white-balance adjustment control signal, and electronic circuitry for receiving image data to be rendered on the flat panel LCD. Further, the flat panel LCD of one embodiment is configured for coupling to a light-sensing device to detect optical characteristics of the flat panel LCD.
According to one embodiment of the present invention, the flat panel LCD comprises a large display area liquid crystal display screen having an aspect ratio that is greater than 1.3:1. In one embodiment, the aspect ratio is substantially 1.6:1, having 1,600 pixels across the horizontal and 1,024 pixels along the vertical. In this embodiment, the flat panel LCD is an SXGA-wide aspect ratio flat panel display monitor having high-resolution for displaying high-information content. This embodiment is particularly well suited for displaying text, graphics and other types of still and/or motion audio/visual works. The wide aspect ratio allows the display of multiple pages, side-by-side, there by facilitating certain tasks such as desktop publishing, pre-press soft-proofing, video and digital photography editing, medical imaging, and graphics animation and design. The flat panel display of the present invention further, includes compensation film layers for providing enhanced off axis viewing capability in the horizontal and vertical axes.
Significantly, the flat panel LCD of one embodiment of the present invention provides white-balance adjustment capabilities. The white balance adjustment mechanisms include the provision of two pairs of light sources of differing color temperature, whose brightness can be independently varied (and distributed through a light distribution mechanism) to adjust color temperature without altering the dynamic range of the grayscale resolution of the RGB colors. The flat panel display of the present invention also provides a white-balance adjustment control input for receiving a white-balance adjustment control signal, and a control circuit responsive to the white-balance adjustment control signal for adjusting color temperature of the display by altering the brightness of the appropriate light sources. In one embodiment of the present invention, a white balance adjustment control signal is generated by the host computer, and is transmitted to the flat panel LCD unit via an inter-integrated circuit (I2C) bus.
According to one embodiment of the present invention, the flat panel LCD monitor is configured for coupling to a digital computer system to receive image data to be rendered on the flat panel LCD monitor, and to receive control signals such as white-balance adjustment control signals and power management control signals. In the present embodiment, a dual-channel low-voltage differential signal (LVDS) interface is used for transmitting image data from the host computer to the flat panel LCD unit. This interface provides sufficient bandwidth for displaying high information content, image data. In one embodiment of the invention, the host computer includes a color look-up table for providing gamma correction to the image data on the fly. One embodiment of the present invention further includes white balance adjustment software and gamma correction software for generating white-balance adjustment control signals and appropriate gamma correction curves. In one embodiment, the host computer further comprises frame-rate time domain modulation circuitry for processing the image data in order to reduce scalloping effects and other visual artifacts.
According to one embodiment of the present invention, light-sensing device comprises a low-cost luminance sensor specially designed for coupling to a flat panel LCD monitor during monitor calibration. The specially designed luminance sensor is not configured for attaching to the flat panel display by suction. Rather, the luminance sensor is configured for attaching to the flat panel display during monitor calibration by non-suction attachment means. By using non-suction type attachment means, optical characteristics of the flat panel LCD monitor are not distorted during monitor calibration.
Significantly, during monitor calibration, luminance values of the flat panel LCD monitor are measured by the luminance sensor. The luminance values are then used to construct the optical characteristics of the flat panel LCD monitor. The constructed optical characteristics are then matched to a set of target, or reference, optical characteristics. The host computer then adjusts the white balance of the flat panel LCD monitor and/or the gamma values of the RGB colors according to any discrepancies between the constructed optical characteristics and the reference optical characteristics until a precise match is achieved. In this way, precise color calibration is achieved in flat panel LCD monitors with an inexpensive luminance sensor.
Embodiments include the above and wherein the large area wide aspect ratio liquid crystal flat panel display screen is non-emissive and further comprises: a first light source of a first color temperature; and a second light source of a second color temperature different from the first color temperature, the first and second light sources positioned to illuminate the wide aspect ratio liquid crystal flat panel display screen with light having a net color temperature that is dependent on an intensity of the first light source and an intensity of the second light source wherein the first and the second light sources alter the net color temperature of the light, within a predetermined color temperature range, by controlling the intensity of the first light source and the intensity of the second light source. Additionally, the flat panel display screen may comprise a light pipe optically coupled to receive light from the first light source and said light source for illuminating the liquid crystal flat panel display screen with the light from the first and second light sources.